Understanding the neuroendocrine pathways controlling female puberty and reproductive function

: key roles of MKRN3 and DNA methyltransferase expression in the murine hypothalamus

Abstract

The hypothalamus is a critical area of the brain whereby neuroendocrine and environmental cues converge to ensure a timely pubertal onset and normal reproductive physiology. Kisspeptin is indispensable in the control of female reproduction. In rodents, the two largest hypothalamic kisspeptin populations reside in the anteroventral periventricular nucleus (AVPV) and the arcuate nucleus (ARC) (AVPVKiss and ARCKiss). These two populations appear to be regulating the pre-ovulatory GnRH/LH surge and pulsatile GnRH secretion, respectively. Inactivating mutations in the MKRN3 gene are the most common genetic defect detected in children with central precocious puberty (CPP). MKRN3 is thought to regulate kisspeptin expression, gating puberty during childhood. In Chapter 1, I demonstrate that Mkrn3 is expressed in AVPVKiss and ARCKiss neurons of juvenile mice, but is almost undetectable in adults. Furthermore, I demonstrate that Mkrn3 represses the rodent Kiss1 promoter activity. In Chapter 2, I use pre-pubertal (PND21) transgenic mice to examine the effect of Mkrn3 overexpression in AVPVKiss neurons on female puberty onset and reproductive physiology. Experimental mice exhibit normal pubertal onset, but display disrupted ovarian cyclicity, coupled with altered ovarian histology and reproductive hormone levels. The rodent estrous cycle is tightly regulated by circadian rhythms synchronised by the suprachiasmatic nucleus (SCN) of the anterior hypothalamus. DNA methylation has been associated with the regulation of the ovarian cycle in Siberian hamsters. In Chapter 3, I employed RNAscope ISH analysis to identify changes in expression of DNA methyltransferase 3a (Dnmt3a) in defined SCN neuronal populations and AVPVKiss neurons of female mice at proestrous and diestrous. I show that Dnmt3a expression significantly increases at diestrous in SCN arginine vasopressin (Avp)-expressing cells. Therefore, rhythmic changes in DNA methylation within these cells may drive ovarian cycle plasticity. Overall, my results provide novel insights into the mechanisms controlling female pubertal timing, estrous cyclicity and reproductive function.

Date of Award	29 Nov 2022
Original language	English
Awarding Institution	University of St Andrews
Supervisor	Javier Tello (Supervisor)